Projectile rotating band

Abstract

A plastic rotating band for a projectile. More particularly, this invention relates to a projectile having a plastic rotating band chemically bonded to the projectile.

Parent Case Text

This is a continuation of application Ser. No. 111,415, filed Feb. 1, 1971, now abandoned.

Description

A rotating band is a ring of material secured to the surface of a projectile. The exterior surface of the rotating band engages the rifling of a gun during a firing and is engraved, thereby imparting spin to the projectile.

Plastic rotating bands have heretofore been employed with projectiles. Plastic rotating bands have not been universally accepted as replacements for metal rotating bands because of several problems associated with the use of such plastic bands. One principal problem encountered with the plastic rotating band has been the difficulty of maintaining the band secured to the projectile either in firing or during flight. Many different technical approaches have been tried to overcome this difficulty.

With the advent of advanced, high muzzle velocity gun systems, the necessity for improved rotating bands has become apparent. We have now discovered that plastic rotating bands chemically bonded to a projectile surface can withstand the complex stresses imposed on the band in the gun during firing and in-flight. Chemical bonding of the plastic rotating band permits use of plastic materials having greatly reduced strength properties as rotating bands as compared to the strength requirements for non-chemically bonded rotating bands. Chemical bonding of plastic rotating bands to a projectile makes possible simple projectile design and reduction or elimination of the band seat resulting in an increased payload. A further advantage of a plastic rotating band is that it reduces barrel wear in the gun system.

The term "chemically bonded" used in this specification with reference to a plastic rotating band bonded to a projectile is defined herein to mean that the plastic bonded to a metal when tested to failure in tension or in shear, fails in the plastic and not at the metal-plastic interface. A simple method to evaluate chemical bonding is to prepare a metal-plastic-metal sample such as a metal-plastic-metal sandwich employing the same metals, plastics, primers and procedures that are to be employed in bonding the plastic to a projectile. After the sample has been prepared it can be tested to failure on an Instron Testing Machine following ASTM or modified ASTM procedures. If, in conducting these tests, the sample fails at the metal-plastic interface, then a chemical bond, as defined herein, has not been achieved. ASTM Tests D638-61T, D732-46 and D1002 can be used to evaluate chemical bonding, as defined herein, using appropriately prepared test samples.

There are numerous plastics which can be chemically bonded to metals and employed as a chemically bonded rotating band within the scope of this invention. Projectiles can be prepared from any metal suitable for use in the gun system in which the projectile is being employed. The particular plastic chosen for use as a rotating band must, of course, be evaluated based on the overall gun system requirements. The chief properties of the plastic material which must be evaluated in addition to those previously defined are bearing strength, slip properties, dimensional stability, ductility, linear coefficient of expansion, abrasion resistance and hardness. The plastic must have a combination of properties permitting the plastic to engrave and obturate the projectile under actual use conditions. Another factor to be considered in choosing a plastic material for a rotating band for a projectile is the type of ammunition round being manufactured. For example, plastic rotating bands for caseless ammunition which are close to or in direct contact with the propellant charge of the caseless round must not absorb propellant ingredients to any significant extent such that a change in properties of either the plastic rotating band or propellant charge results. Cased rounds wound not necessarily be subject to these same limitations. Also, it is absolutely necessary that the plastic rotating band be chemically compatible with the composition of the propellant charge.

The strength of the plastic rotating band of this invention must be sufficient to withstand the loads imposed on the band without breaking as the projectile passes through the gun barrel wherein the rotating band becomes engraved in the riflings of the gun and imparts the stabilizing spin to the projectile leaving the gun muzzle. Plastic materials must also have sufficient tensile strength to prevent the band from breaking in-flight.

Plastic materials which can be chemically bonded to the surface of a projectile include both thermoplastic and thermosetting polymers. Thermoplastic materials are preferred. Thermosetting resins which are not highly crosslinked can be employed. Highly crosslinked thermosetting resins have insufficient ductility to engrave and obturate the projectile satisfactorily. The plastic material employed as the rotating band of this invention, i.e., thermoplastic or thermosetting polymers, can contain fillers to alter the properties of these plastics as necessary. A particularly suitable filler material is fibrous glass. The plastic material can also be foamed to alter the properties of the plastic materials. The foamed structure can be filled with other ingredients such as lubricants, useful in operation of the gun system.

Illustrative plastic materials which can be chemically bonded to the surface of the projectile for use either in conventional ammunition or caseless ammunition wherein the plastic band is in contact with a propellant charge of the single, double or triple base compositions include acetal resins, ethyl cellulose, epoxy resins, polychlorotrifluoroethylene, fluorinated ethylenepropylene resins, polyvinylidene fluoride, polyacrylonitrile, nylons; polyolefins including, polyethylenes, polybutylenes, polypropylene, polymethylpentenes, polyolefin copolymers such as those derived from ethylene and propylene and the like; polyvinyl chloride, polyvinylidene chloride, chlorinated polyvinyl chloride and vulcanized fibers. For conventional ammunition or caseless ammunition where the propellant charge is unplasticized nitrocellulose, additional plastic materials which can be chemically bonded to the projectile include polycarbonates, polysulfones, modified polyphenylene oxide, styrene-acrylonitrile, copolymers, acrylonitrile-butadiene-styrene terpolymers (ABS resins), ABS modified polyvinyl chloride, ABS-polycarbonate alloys, acrylic polymers, cellulose acetate, polyesters, and polyvinylbutyral. The foregoing list of plastics is not all inclusive of polymers which can be bonded to metals in preparing the plastic rotating bands of this invention. For any particular gun system plastics must be evaluated based on the plastic evaluation criteria heretofore described for the conditions of actual use.

The projectile of this invention having a plastic rotating band chemically bonded to the surface can be prepared by several methods. In any of the methods employed, the surface of the projectile to which the rotating band is to be bonded, referred to herein as the projectile band seat surface, is first cleaned very carefully. The projectile band seat surface can be roughened such as by sand blasting to aid in bonding of the plastic thereto. A primer material is then applied to the clean projectile band seat surface. The priming material employed varies with the particular plastic material which is being used as the projectile rotating band. The primed projectile is then heated to a temperature above the melting point of the plastic which is to be applied. The plastic is then applied to the hot projectile surface and fused. The plastic coated projectile is then cooled. The heating step can be repeated to alter the thickness of the projectile band. A particularly suitable method for applying a plastic rotating band to a projectile is injection molding. Other methods such as spraying and fluidized bed methods can be employed. The plastic rotating band can be preformed and chemically bonded to the projectile, if desired. The chemically bonded plastic rotating band can be machined, if necessary, to a desired configuration.

This invention is more fully illustrated in the drawings and the examples which follow. In the drawings, like numbers are used for like parts where applicable.

FIG. 1 is a side view of a projectile having no rotating band. FIG. 2 is a side view of a projectile partly broken away and in section illustrating the projectile of FIG. 1 having a plastic rotating band bonded thereto. FIG. 3 is an enlarged view illustrating the rotating band configuration of the projectile of FIG. 2 before firing. FIG. 4 is a side view of the projectile of FIG. 2 as it appears after a firing. FIG. 5 illustrates another projectile having a chemically bonded rotating band. FIG. 6 is an enlarged view illustrating the configuration of the rotating band of FIG. 5 before firing. FIG. 7 is a side view of the projectile of FIG. 5 as it appears after a firing. FIG. 8 illustrates another embodiment of a chemically bonded plastic rotating band.

In FIG. 1 a projectile body 10 is shown having a rotating band seat surface 12. The band seat depth 14 in the projectile necessitates making the aft-end of the projectile of heavier guage steel to withstand the forces on the projectile during firing resulting in a decreased payload which can be carried within the envelope defined by the exterior surface of the projectile body 10. The configuration of a plastic rotating band 16 chemically bonded to the rotating band seat surface 12 is shown in FIG. 2. The outermost exterior surfaces of the rotating band referred to herein as the rotating band ribs 18 engage the rifling in the gun in which the projectile is fired. Groove 20, oftentimes referred to as a cannelure, behind ribs 18 of the rotating band 16 provides space for flow of plastic during engraving. The free volume envelope 22 aft of the forward surface of the projectile rotating band is shown in FIG. 3 in dotted lines. FIG. 4 shows excellent engraving of the plastic rotating band as it appears from in-flight photographs taken from actual firings.

The projectile 23 shown in FIG. 5 has a greatly reduced band seat depth 24 as compared to the band seat depth 14 for projectile 10 illustrated in FIGS. 1, 2 and 3. The volume shown by envelope 29 aft of the forward surface of the rotating band is the sum of the free volume provided by the cannelures and the volume aft of the rotating band to the aft-end of the projectile. FIG. 6 further illustrates the band configuration of FIG. 5. The excellent engraving of the plastic rotating band of FIG. 5 as actually seen from high speed photographs is illustrated in FIG. 7.

FIG. 8 illustrates another embodiment of the projectile of this invention having a plastic rotating band chemically bonded thereto. In this embodiment, projectile 30 has no band seat whatsoever. Plastic rotating band 32 is chemically bonded directly to the projectile surface.

The following examples illustrate one method of preparation of the projectile of this invention having a plastic rotating band chemically bonded thereto, and firing results achieved with these projectiles.

EXAMPLE 1

A 25 millimeter steel test projectile weighing 3206 grains is sanded to remove rust and any other foreign material. After standing, the projectile is degreased using a clean trichloroethane dampened cloth. Surface preparation of the metal is completed by immersing the projectile in a mixture comprising 3 parts of water to 1 part of No. 11 deoxidizer compound which is of the phosphoric acid type and is per MIL-M-10578B. The projectile is immersed in the mixture for 5 minutes, is removed from the mixture, rinsed with hot water and dried. Prior to priming of the projectile band seat surface, the projectile is again degreased using a clean trichloroethane dampened cloth. A primer is prepared by dissolving an ethylene-acrylic acid copolymer, in hot xylene at 130.degree.C. to form a 4% by weight solution of the copolymer. The ethylene-acrylic acid copolymer employed contains 15% by weight of acrylic acid, has a density of 0.949 grams/cc, a melt index of 50 per ASTM D-1238, a VICAT softening point of 63.degree.C., a DTA softening point of 63.degree.C., a tensile strength of 2000 psi, an ultimate elongation of 550% and a modulus of 8,800 psi. The priming solution is held at 130.degree.C. at which temperature all of the copolymer dissolves in xylene. The projectile which is at ambient temperature is immersed in the primer solution for from about 2 to about 3 seconds. The primer-wet projectile is then placed in an oven at 150.degree.C. to remove xylene solvent. A high density polyethylene having a molecular weight of between 300,000-600,000 is applied in the form of tiny pellets to the primed projectile band seat surface. The projectile band seat surface extends for 1.0 inch along the exterior surface of the projectile. The tiny pellets of the high molecular weight polyethylene adhere to the primed metal surface and the projectile is placed in an oven at 150.degree.C. for about 10 minutes until the pellets are fused. Additional polyethylene pellets are then added to fused pellets and the projectile is returned to the 150.degree.C. oven until the additional pellets are fused. This procedure is repeated until the desired rotating band thickness is achieved. The projectile is then removed from the oven and the entire projectile is quenched with cold tap water. The plastic band is then machined to the configuration illustrated in FIG. 2.

EXAMPLE 2

The projectile having the rotating band of high density polyethylene prepared as described in Example 1 and having a configuration as shown in FIG. 2 is fired in a 25 millimeter gun having a uniform twist rifling, said rifling making an exit angle of 8.degree. and 55 minutes with the barrel of the gun. The projectile muzzle velocity is measured at 3360 feet per second. High speed photographs are taken of the projectile in-flight. Rifling marks are visible on the band and all data indicate that the projectile was spinning properly. The photographs show that the plastic bands engraved well and the bands were fully retained in-flight. FIG. 4 is a drawing of the projectile in-flight as it appears from high speed photographs.

EXAMPLE 3

Two 25 millimeter steel projectiles having the rotating band groove depth of 0.026 and 0.052 inches, respectively, said grooves being spaced 0.25 inches from the aft-end of the projectile are sanded to remove rust and other foreign materials. After sanding, the projectiles are degreased using a trichloroethane dampened cloth. Surface preparation is completed by immersing the projectile in a mixture comprising 3 parts of water and 1 part of No. 11 deoxidizer compound of the phosphoric acid type per in MIL-M-10578B. The projectile is maintained immersed within this solution for 5 minutes, is removed from the solution, rinsed with hot water, and dried. The projectile is again degreased using a trichloroethane dampened cloth. A priming solution is prepared by dissolving a maleic anhydride modified polymer of propylene in xylene at 120.degree.C. to form a 2% by weight solution of the polymer. This polymer of propylene is prepared by chemically combining solid propylene polymers with from about 0.05 to about 5% by weight of maleic anhydride. The projectiles are heated to 200.degree. C. and are immersed in the priming solution for from about 2 to about 3 seconds and placed in an oven held at 200.degree.C. for about 5 minutes to remove the xylene solvent. Powdered polypropylene having an average particle size of 35 microns is dusted on the hot primed surface. The projectile is placed in an oven at 200.degree.C. to fuse the polypropylene powder. Additional polypropylene is added to the surface of the fused polypropylene and the heating and fusing procedure is repeated until a rotating band having a thickness of 0.075 inches results. The projectile is removed from the oven and the entire projectile is quenched using large amounts of cold tap water which is poured over the internal and external walls of the projectile body. The plastic band is then machined to the rotating band configuration illustrated in FIG. 6.

EXAMPLE 4

Two projectiles having polypropylene rotating bands chemically bonded thereto following the procedure set forth in Example 3 and having the band configuration of FIG. 6 are fired in a 25 millimeter gun. The barrel of the gun has a uniform twist rifling which makes an exit angle of 8.degree. and 55 minutes with the barrel. Muzzle velocity of the projectiles is from 3600 to 3700 feet per second. High speed photographs are taken of these projectiles in-flight. These photographs show that all the projectiles are stable in-flight, with very small yaw angles and yaw damping. These photographs also show that the polypropylene rotating bands engrave well and are fully retained in-flight.

For optimum use of a projectile having a chemically bonded rotating band, the configuration of the plastic rotating band is important. The plastic rotating band chemically bonded to the surface of the projectile should have sufficient free volume aft of the forward edge of the rotating band to permit flow of the plastic into this area during the engraving process. As the projectile travels through the barrel of the gun, the plastic material engraves and flows into the free volume aft of the forward surface of the rotating band. If insufficient free volume is provided to accept this flow of plastic material, excess pressure can build up in the gun which can result in excessive barrel wear, unsatisfactory ballistics, rotating band failure and possibly gun failure.

From the foregoing discussion it is obvious that the plastic material chosen for any particular gun system must have sufficient ductility to flow under the conditions encountered within the gun. If there is insufficient ductility in the plastic material employed, the plastic rotating band can crack or break-up resulting in failure of the projectile to be stabilized in-flight, causing failure of the projectile to be fired in the desired trajectory.

As will be evident to those skilled in the art, various modifications can be made or followed in view of the foregoing disclosure and discussion without departing from the spirit or scope of the disclosure or from the scope of the claims.

Claims

What we claim and desire to protect by Letters Patent is:

1. A metal projectile having a high density polyethylene rotating band secured to the surface of the metal projectile, the intersection of the surface of the metal projectile and the polyethylene rotating band defining an interface, said polyethylene rotating band being secured to the metal projectile solely by a chemical bond formed between the metal projectile and a primer and between the primer and polyethylene rotating band at the metal projectile-rotating band interface, said primer being prepared from a solution comprising ethylene-acrylic acid copolymer, said chemical bond having a strength such that the chemically bonded polyethylene rotating band when tested to failure in tension or in shear fails in the polyethylene rotating band rather than at the metal projectile-rotating band interface.

2. A metal projectile having a polypropylene rotating band secured to the surface of the metal projectile, the intersection of the surface of the metal projectile and the polypropylene rotating band defining an interface, said polypropylene rotating band being secured to the metal projectile solely by a chemical bond formed between the metal projectile and a primer and between the primer and polypropylene at the metal projectile-rotating band interface, said primer being prepared from a solution of a maleic anhydride modified polymer of propylene prepared by chemically combining solid propylene polymers with from about 0.05% to about 5% by weight of maleic anhydride, said chemical bond having a strength such that the chemically bonded polypropylene rotating band when tested to failure in tension or in shear fails in the prolypropylene rotating band rather than at the metal projectile-rotating band interface.